[Webkit-unassigned] [Bug 86071] Incorrect behavior of upright text in vertical writing modes

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=86071





--- Comment #7 from Koji Ishii <kojiishi at gmail.com>  2012-05-16 02:57:32 PST ---
Thanks for the clarifications. I looked into further.

#2 turned out to be a bug in CTFontGetVerticalTranslationsForGlyphs. This API supposed to return vertical origins, but its X component of return value is incorrect for some glyphs (probably proportional glyphs?) if the font has vertical metrics. We could either wait OS X to fix this bug, or disregard X position of the returned value and calculate by ourselves.

Note that the API returns values for font-size of 1 on Snow Leopard and we have a workaround for the bug, but this bug reproduces on both Snow Leopard and Lion. Also note that this looks good on iOS Safari, maybe iOS doesn't use the API, or the API on iOS doesn't have the bug.

#4 is complex code path + upright combination. The current implementation really doesn't support this combination well.

#5 shows different results by builds. A patch was landed to switch to the complex code path by setting any font feature settings on last August, so it used to behave the same as #2 but it's now the same issue as #4.

On OS X, complex code path + upright hits CT bug. On Windows, it hits Uniscribe limitations. This is a separate issue from #2. We could either workaround not to use these APIs on such cases, or wait for these APIs to fix.

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